Number 4 misfires at idle after intake gasket was replaced

run the fault codes to find the misfire problem

I don't think you really understand what this fault code means, it means that likely all the engine cylinders are misfiring at random no set pattern, not any particular cylinder. I would start with checking for engine vacuum leaks like the intake manifold gasket. that is all I can say since you provided no make, model or year and engine type and size information.

have a compression test done and look for a moving valve seat insert
it gives the knock, misfire
as it is no 2 cylinder it is mechanical because you have moved the injectors and coils , plugs and leads and it stays at no 2 cylinder
If you want clean engine oil then change the synthetic oil out and put in diesel oil 20w40
It will not harm the engine as it is the same as petrol oil but with more additives than petrol oil
it is cheaper and has heavy detergent properties that keeps the engine internals clean
from the gunk in the sump ,it is clear that changing engine oil on a regular basis is something you don't do but if you want a reliable long lasting engine , it is must do number 1

Hi
The misfire could be being caused by a number of things, such as:
1. Worn/dirty spark plug - Clean/replace spark plug/s
2. Spark plug lead breaking down - Replace spark plug lead
3. Or possibly the intake gasket. If the intake gasket is leaking it causes a vacuum leak. with this vacuum leak at idle it will cause a misfire. - To check this, take a can of carb cleaner (or WD-40 may also work) and when the car is running, spray it along the intake by cylinder number If you see/hear the engine change then you have a leaking intake gasket.
Trust this helps
Alan

Please go to this link and read about the causes and the solutions for engine misfires.

Change oil,replace spark plugs and fuel filter,air filter,check all brakes and lube caliper slides,check and flush cooling system,replace trans filter and gasket and perform a trans flush.This will replace all the trans fluid not just the fluid in the trans pan.Add fuel injector cleaner about every oil change.This will keep this vehicle going for another 100k.This is the best engine G.M. has had and will go over 300k.The biggest problem was the upper intake plenum gasket leaking coolant into the cylinders and oil system.Hope this has helped and good luck.

My guess on this is gonna be a cracked ignition coil. Have it tested by someone. It is very common for these coils to crack and cause a misfire.

I also have the same problem with my 2002 caravan 3.3L. Misfire on cylinder #5 (P0305). Replaced ignition plugs & wires, intake manifold gasket, plenum gasket, fuel filter, air filter, cleaned fuel injectors, swapped fuel injector #5 to #1. After all these, I have no more DTC code but the symptom of misfire is still there, the idle is rough and I can feel the misfire even if I step on the gas when in park or neutral. Please let me know what to do next. Thanks!

intake gasket blown

hello before you replace parts you might not need try to test the map sensor see if it is within range this works with vacuum changes in motor goodluck please rate